It is proposed to isolate pure phosphoglycerate kinase (PGK) and enolase from several tissues of young and old rats and determine if there are age-related differences in the properties of the respective enzymes. Initial results show substantial differences in stability and spectral properties between "young" and "old" muscle PGK. On the other hand, muscle and liver enolases show no age-related alterations. In preliminary results, "old" heart enolase shows increased heat-lability. Studies will continue on the differences in conformation found in enolase from young and old Turbatrix aceti. This nematode enzyme has proved to be an excellent model for studies of age-related changes. An attempt will be made to interconvert "young" and "old" forms of the enzyme by unfolding the protein chains of the respective enzymes by treatment with urea or guanidine and subsequently permitting refolding. If successful, the experiments will prove unequivocally that the altered properties of "old" nematode enolase are due to conformational changes resulting from a subtle denaturation of the "young" enzyme rather than from covalent or sequence changes.